Fix RTCAudioSession crash in removeDelegate.

webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 129 matching lines @@
   }
 }
 
 - (void)removeDelegate:(id<RTCAudioSessionDelegate>)delegate {
   if (!delegate) {
     return;
   }
   @synchronized(self) {
     _delegates.erase(std::remove(_delegates.begin(),
                                  _delegates.end(),
-                                 delegate));
+                                 delegate),
+                     _delegates.end());
     [self removeZeroedDelegates];
   }
 }
 
 - (void)lockForConfiguration {
   _crit.Enter();
   rtc::AtomicOps::Increment(&_lockRecursionCount);
 }
 
 - (void)unlockForConfiguration {
@@ skipping 352 matching lines @@
 
 // TODO(tkchin): check for duplicates.
 - (void)pushDelegate:(id<RTCAudioSessionDelegate>)delegate {
   @synchronized(self) {
     _delegates.insert(_delegates.begin(), delegate);
   }
 }
 
 - (void)removeZeroedDelegates {
   @synchronized(self) {
-    for (auto it = _delegates.begin(); it != _delegates.end(); ++it) {
-      if (!*it) {
-        _delegates.erase(it);
-      }
-    }
+    _delegates.erase(
+        std::remove_if(_delegates.begin(),
+                       _delegates.end(),
+                       [](id delegate) -> bool { return delegate == nil; }),
+        _delegates.end());
   }
 }
 
 - (int)activationCount {
   return _activationCount;
 }
 
 - (int)incrementActivationCount {
   RTCLog(@"Incrementing activation count.");
   return rtc::AtomicOps::Increment(&_activationCount);
@@ skipping 208 matching lines @@
 - (void)notifyDidUnconfigure {
   for (auto delegate : self.delegates) {
     SEL sel = @selector(audioSessionDidUnconfigure:);
     if ([delegate respondsToSelector:sel]) {
       [delegate audioSessionDidUnconfigure:self];
     }
   }
 }
 
 @end